We all know how fun and exciting Cyrodiil is, at least it is for me whenever am fighting for my life in there... but here is some thoughts for other kinds of PvP.
Once hitting let us say level 50 plain out people would be able to visit areas all over running into players of the other faction and the likes... etc. etc.
Here is the suggestion, that would actually spice the game at least if you endure more sides of it as it is.
Be able to go special forces by eg. /pvp and /pvpoff (going /pvpoff would have a 10min cooldown before not flagged anymore) or something... that way there can advance free form PvP in normal zones we can make playermade events and so on and so forth without having to evolve into dekadent arena alike stuff.
Think about it, besides of fighting in the campaign there is other options once needing to break from it weather it is a playermade event or random skirmishes here and there in eg. Wayrest or Auridon.... stirring up bar fights and such...
Personally I think alot of fun could be had in a way like this, at least it is constructive and even give players more choices.
Make it so Assault/Support tree only work inside cyrodiil though, which could really make it fun.